Home Brew 2
I think I need to make one point clear from my previous post. The ball bearings are still taking all thrust loads present. The thrust bearings (fancy name for washers) are there to spread the load evenly and transfer it to the center race of the ball bearing. I looked for washers with very accurate center holes and found them in the form of thrust bearings. I even considered making my own washers as precision washers are hard to find in small quantities. Thrust washers are not hard to find in small quantities. The thrust washer also protects the bearing… Continue reading
I modified the two Y screws on HB2 this evening. I removed the axis screws completely from the machine and chucked them (one at a time) into my Proxxon PD400 lathe. I cut back the 0.250″ diameter shafts at each end an additional 0.063″ – 0.065″ to make space for the 1/16″ thick 1/4″ x 5/8″ hard bronze thrust washers. I also made sure the screw shoulder was absolutely flat to the washer and square to the shaft.
I reassembled all four Y axis ball bearings (new) with a hard bronze thrust bearing (Alloy 932, sae 660) between the shaft and the ball bearing. The flat thrust… Continue reading
I am having some thoughts that the HB2 stepper problem may be part of the stepper resonance phenomena. The two Y axis motors on separate channels but running in tandem may be creating a mechanical resonance between them. Kind of like tuning both engines to the same RPM in a twin piston engine aircraft. There is a “beat note” low frequency resonance between the engines as they approach the same speed. (I am a pilot.) The same effect occures in a twin engine boat.
The same holds true when tuning a CW frequency in amateur radio. Another frequency (BFO –Beat Frequency… Continue reading
Here are the pictures of both pair of Y axis bearings. The drag I suspected wasn’t on the outside case edge but right in the middle of the shields. I most likely started this problem when I was experimenting with end thrust. I have replaced these but not tested the new bearings yet. I’ll do that this weekend.
I found a source for some 1/16″ thin solid thrust washers if I have to use them. They are available in several types of material and the center hole is very accurate.
One shield shown here is actually dented. I don’t know… Continue reading
Broke a coupling again, one of the new ones. So the new coupling isn’t any stronger than my original design. This time it was in the X axis where there has never been a problem. I replaced a perfectly good original style coupling with the new one and the trouble began.
This kind of “random error” coupling failure has been driving me crazy, especially now in a place where it has never been an issue. It is a good example of how powerful the stepper motors are at low speeds. They can break things well above their holding torque ratings.… Continue reading